Material for making hyper frequency multi-layer chip inductors with high performance and low sintering temperature and a process for preparing the material

ABSTRACT

A composition of material used for making hfMLCIs having a sintering temperature below 1000°. The composition comprises a major component and a minor component, said major component being a general formula: Ba 3 Co 2-x-y Zn x Cu y Mn x Fe 24-z-w O 41,  wherein x, z, w,=0-1.0 and y=0-0.8, and said minor component comprising at least one compound selected from the group of Bi 2 O 3 , V 2 O 5 ,PbO,B 2 O 3 , Lif and CaF 2 . HfMLCIs made from the composition of the present invention are capable of functioning in the frequency region of 300-800 MHz.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a new material used in manufacturing surface mounting devices and a process of making said material. Particularly, the invention pertains to a material for making high performance hyper frequency multi layer chip inductors, which can be sintered at a low temperature.

[0003] 2. Description of the Related Art

[0004] Multilayer chip inductors (“MLCI”), also known as multilayer ferrite inductors (“MLFI”), are one of the most important surface mounting devices (“SMDS”). The key technical aspect is the co-firing between ferrite and an internal conducting material, such as silver (Ag, chosen for its good conductivity and lower costs). It requires the ferrite to have a low sintering temperature and a high initial permeability. The main materials currently available for manufacturing SMDS are Ni—Zn—Cu ferrite sintered at 850-900° C. and low dielectric constant ceramics. The Ni—Zn—Cu ferrite, has a resonant frequencies below 200 MHz, which may reach 300 MHz if Zn is excluded from the ferrite. Thus, Zi—Zn—Cu ferrite is not suitable for making MLCIs operating in hyper frequencies (300-1000 MHz). On the other hand, low dielectric constant ceramics, with a permeability equal to 1, has been used for making MLCIs operating in ultra high frequencies (>800 MHz), where high inductance is not required. Therefore, there is no ideal material for making MLCI operating in the frequency region from 300-800 MHz.

[0005] In 1950's, Philip developed Co₂Z hexaferrite (Ba₃Co_(z)Fe₂₄O₄₁). It generally has a high sintering temperature (^(˜)1300° C.). Recently, it was found that using a chemical synthetic method with citrate precursor could be used to prepare Co₂Z hexaferrite with a lower formation temperature (^(˜)1150° C.). The chemical synthetic method also improves compositional homogeneity, which is particularly important for doping elements. However, to the applicants' knowledge, no one has taught or suggested any CO₂Z hexaferrite which can be sintered at a temperature below 900° C.

SUMMARY OF THE INVENTION

[0006] The present invention discloses a new material composition used in making high performance hyper frequency multiplayer chip inductors (“hfMLCI”) and a process of preparing said composition. The composition of the present invention can be sintered under 900° C. so that the hfMLCI made from this material is suitable for the frequency region of 300-1000 MHz with better inductance and reliability, and can be manufactured with relative lower costs.

[0007] The composition of the present invention has a major component and minor component. The major component accounts for 88-99% by weight and the minor component accounts for 1-12% by weight. The major component is Z-type planar hexaferrite having a general formula of Ba₃Co_(2-x-y)Zn_(x)Cu_(y)Mn_(z)Fe_(24-z-w)O_(41-3/2(z+w)), wherein 0≦x≦1.0, 0≦y≦0.8, 0≦z≦1.0 and 0≦w≦1.0. The minor component acts as a sintering aid, having a formulation of aBi₂O₃+bV₂O₅+cPbO+dB₂O₃+eLiF+fCaF₂, where 0≦a≦1, 0≦b≦1, 0≦c≦1, 0≦d≦1, 0≦e≦1, 0≦f≦1.

[0008] The composition of the present invention can be prepared by following the steps described below:

[0009] (1) weigh out each salt to prepare a solution contain Fe³⁺, Co²⁺, Ba²⁺, Zn²⁺, Cu²⁺, Mn²⁺ in predetermined molar ratios, with Fe³⁺'s concentration being 0.4-5 M;

[0010] (2) dissolve Fe³⁺ salt in water and add NH₄OH of an equal molar number to precipitate Fe(OH)₃, collect Fe(OH)₃ by filtration and wash it with water, and then dissolve the freshly prepared Fe(OH)₃ in a citric acid solution (Fe³⁺/citric acid mole ratio should be 1-2) at 60-80° C. with stirring until the solution becomes transparent;

[0011] (3) add all the remaining salts weighed out in step (1), that is, all the salts except Fe3+, to the solution prepared in step (2), add NH₄OH to adjust the pH to 6.0-8.0, and wait for about 2 hours until the solution becomes sol;

[0012] (4) incubate the sol obtained in step (3) in an oven at 130-150° C. until it dries up;

[0013] (5) heat-treat the dried-up gel at 900-1250° C. for 2-6 hours to obtain Z-type hexaferrite powder;

[0014] (6) mix the Z-type hexaferrite powder with the sintering aids, i.e., the minor component of a predetermined formulation, grind the mixture in water or alcohol in a ball mill;

[0015] (7) dry up the ground mixture at 80-120° C., sieved and press into pellets; and

[0016] (8) sinter the pellets at 900-1250° C. to obtain the composition of the present invention.

[0017] It is also contemplated that the above described procedure can be varied without departing the present invention. For example, although the above procedure stated that Fe³⁺ was first precipitated with NH₄OH before mixing with the other salts weighed out in step (1), it is possible that Fe3+ is first mixed all the other salts in a solution and then added with citric acid and NH₄OH, with the resulting solution being used to continue in steps (4)-(8). Another possible variation lies in step (6). While in the above specified procedure the Z-type hexaferrite powder obtained in step (5) is first mixed with the sintering aids before grinding in a ball mill, it is entirely possible that the Z-type hexaferrite is ground alone and dispersed into ethylene glycol and then mixed with a solution of the sintering aids which, after adjusting the pH, forms a hydroxide coating on the surface of the Z-type hexaferrite particles.

[0018] Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the description and drawings are provided solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the claims.

[0019] The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.

[0020] Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In the drawings, like reference characters denote similar elements throughout the several views:

[0022]FIG. 1 depicts the relationship between the permeability and the frequency for samples 1-1,1-2, and 1-3 made according to the present invention.

[0023]FIG. 2 depicts the relationship between the quality factor and the frequency for samples 1-1,1-2, and 1-3 made according to the present invention.

[0024]FIG. 3 depicts the relationship between the permeability and the frequency for samples 2-1,2-2, 2-3,2-4, 2-5,2-6, 2-7, and 2-8 made according to the present invention.

[0025]FIG. 4 depicts the relationship between the quality factor and the frequency for samples 2-1,2-2, 2-3,2-4, 2-5,2-6, 2-7, and 2-8 made according to the present invention.

[0026]FIG. 5 depicts the relationship between the permeability and the frequency samples 3-1,3-2, 3-3, and 3-4 made according to the present invention.

[0027]FIG. 6 depicts the relationship between the quality factor and the frequency for samples 3-1,3-2, 3-3, and 3-4 made according to the present invention.

[0028]FIG. 7 depicts the relationship between the permeability and the frequency samples 4-1,4-2, and 4-3 according to the present invention.

[0029]FIG. 8 depicts the relationship between the quality factor and the frequency for samples 4-1,4-2, and 4-3 made according to the present invention.

[0030]FIG. 9 depicts the relationship between the permeability, the quality factor and the frequency for samples 5-1 and 5-2 made according to the present invention.

[0031]FIG. 10 depicts the relationship between the permeability, the quality factor and the frequency for samples 6-1 and 6-2 made according to the present invention;

[0032]FIG. 11 depicts the relationship between the permeability, the quality factor and the frequency for samples 7-1 and 7-2 made according to the present invention;

[0033]FIG. 12 depicts the relationship between the permeability, the quality factor and the frequency for samples 8-1 and 8-2 made according to the present invention;

[0034]FIG. 13 depicts the relationship between the permeability, the quality factor and the frequency for samples 9-1 and 9-2 made according to the present invention

[0035]FIG. 14 depicts the relationship between the permeability, the quality factor and the frequency for samples 10-1 and 10-2 made according to the present invention.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

[0036] Property Measurement

[0037] The magnetic properties were measured using a HP 4291B RF impedance analyzer from 1 MHz to 1800 MHz. The d.c. resistivity at room temperature was measured by HP 4140B using disk sample with silver paste on both sides. The magnetic temperature characteristics were measured at 4 MHz with a HP 4192A LF impedance analyzer at temperatures ranging from −50° C. to 150° C.

EXAMPLE 1

[0038] In this embodiment, the material composition is to be made from substantially pure Co₂Z hexaferrite as the major component and Bi₂O₃ as the minor component (sintering aid). 96.96 grams of Fe(NO₃)₃.9H₂O are dissolved in water and an appropriate amount of NH₄OH is added to the solution to precipitate Fe(OH)₃. The Fe(OH)₃ precipitate is then dissolved in a solution containing 55 grams of citric acid. Upon the citric acid solution becoming transparent, 5.82 grams of Co(NO₃)₂.6H₂O and 7.68 grams of Ba(CH₃COO)₂ are added. After adjusting the pH to 6-8, the solution becomes a dark-brown sol, which is dried up and calcined at an appropriated temperature to produce dark Co₂Z (Z-type hexaferrite) in formula Ba₃CO₂Fe₂₄O₄₁ powder 20 grams of the Co₂Z powder and an appropriate amount of Bi₂O₃ are mixed so that the ratio of Co₂Z over Bi₂O₃ is 93:5 by weight. The mixture is ground with iron balls, dried, and pressed into either a disk form or a toroidal form (disks with a outside diameter of 10 mm and a thickness of 1 mm, formed under a pressure of about 2 MPa, or toroidals with a outside diameter of 20 mm, an inside diameter of 10 mm and a thickness of 3 mm, formed under a pressure of about 7 MPa). The disks or toroidals are sintered at 890° C. (sample 1-1), 920° C. (sample 1-2) or 950° C. (sample 1-3).

[0039] Referring to FIG. 1 and FIG. 2, the initial permeability and quality factor over a range of frequencies are shown for samples 1-1,1-2 and 1-3. FIG. 1 shows that for all the samples the initial permeability is above 4 and the cut-off frequency is above 1800 MHz. FIG. 2 shows that the quality factor at 300 MHz is around 40 for all the samples. The main electric-magnetic properties of the samples are summarized in Table 1, where μ_(i) is initial permeability, Q is quality factor, (α_(μ))_(rel) is relative temperature coefficient of inductance, and ρ is insulation resistivity. TABLE I Sample Condition μ_(I) Q (300 MHz) (α_(μ))_(rel)(/° C.) ρ (Ω · cm) 1-1 890° C./6 h 3.7 40 1.5 × 10⁻⁶ 4.4 × 10⁸ 1-2 920° C./6 h 3.8 42 9.8 × 10⁻⁷ 6.1 × 10⁸ 1-3 950° C./6 h 4.6 50 1.7 × 10⁻⁶ 5.8 × 10⁸

EXAMPLE 2

[0040] This embodiment is similar to the one described above. The difference lies in the minor component, which is a mixture of compounds, not a single compound as used in Example 1. The minor component in this embodiment comprises Bi₂O₃, LiF and CaF₂ (1:1:1 by weight). 96.96 grams of Fe(NO₃)₃.9H₂O are dissolved in water and an appropriate amount of NH₄OH is added to the solution to precipitate Fe(OH)₃. The Fe(OH)₃ precipitate is then dissolved in a solution containing 55 grams of citric acid. Upon the citric acid solution becoming transparent, 5.82 grams of Co(NO₃)₂.6H₂O and 7.68 grams of Ba(CH₃COO)₂ are added. After adjusting the pH to 6-8, the solution becomes a dark-brown sol, which is dried up and calcined at an appropriated temperature to produce dark Co₂Z (Z-type hexaferrite Ba₃CO₂ Fe₂₄O₄₁) powder. 20 grams of the CO₂Z powder and an appropriate amount of the above defined minor component (a complex of Bi₂O₃, LiF and CaF₂) are mixed so that the weight percentage of the minor component is 1.0 (sample 2-1), 1.5 (sample 2-2), 2.0 (sample 2-3), 2.5 (sample 2-4), 3.0 (sample 2-5), 4.0 (sample 2-6), 6.0 (sample 2-7), or 10.0 (sample 2-8). The mixture is ground with iron balls, dried, and pressed into either a disk form or a toroidal form (disks with a outside diameter of 10 mm and a thickness of 1 mm, formed under a pressure of about 2 MPa, or toroidals with a outside diameter of 20 mm, an inside diameter of 10 mm and a thickness of 3 mm, formed under a pressure of about 7 MPa). The disks or toroidals are sintered at 890° C.

[0041] Referring to FIG. 3 and FIG. 4, the initial permeability and quality factor over a range of frequencies are shown for samples 2-1,2-2, 2-3,2-4, 2-5,2-6, 2-7 and 2-8. FIG. 3 shows that the maximum permeability can be obtained when the minor component accounts for 1.5%. FIG. 4 shows that the quality factor at 300 MHz reaches 40 for all the samples. The main electric-magnetic properties of those samples are summarized in Table 2, where μ_(i) is initial permeability, Q is quality factor, (α_(μ))_(rel) is relative temperature coefficient of inductance, and ρ is insulation resistivity. TABLE II Sample Condition μ_(I) Q (300 MHz) (α_(μ))_(rel)(/° C.) ρ (Ω · cm) 2-1 890° C./6 h 4.4 50 5.2 × 10⁻⁶ 1.9 × 10⁸ 2-2 890° C./6 h 4.8 55 1.2 × 10⁻⁶ 1.3 × 10⁸ 2-3 890° C./6 h 4.5 50 1.6 × 10⁻⁶ 2.3 × 10⁸ 2-4 890° C./6 h 4.6 52 7.9 × 10⁻⁷ 2.8 × 10⁸ 2-5 890° C./6 h 4.4 45 1.1 × 10⁻⁶ 2.9 × 10⁸ 2-6 890° C./6 h 4.0 54 5.8 × 10⁻⁷ 2.5 × 10⁸ 2-7 890° C./6 h 3.7 50 9.3 × 10⁻⁷ 3.2 × 10⁸ 2-8 890° C./6 h 3.5 50 1.3 × 10⁻⁶ 4.4 × 10⁸

EXAMPLE 3

[0042] This embodiment, as in Example 2, uses a complex minor component comprising Bi₂O₃, LiF and CaF₂ (ratio is 1=1=1 by weight). 80.41 grams of FeC₆H₅O₇. 5H₂O are dissolved in water. To the solution, 5.82 grams of Co(NO₃)₂.6H₂O and 7.68 grams of Ba(CH₃COO)₂ are added. After adjusting the pH to 6-8 with citric acid and NH₄OH, the solution becomes a dark-brown sol, which is dried up and calcined at an appropriated temperature to produce dark Co₂Z (Z-type hexaferrite in formula Ba₃CO₂Fe₂₄O₄₁) powder. 20 grams of the Co₂Z powder and an appropriate amount of the above defined minor component (a complex of Bi₂O₃, LiF and CaF₂) are mixed so that the minor component accounts for 2% by weight. The mixture is ground with iron balls, dried, and pressed into either disks or toroidals (disks with a outside diameter of 10 mm and a thickness of 1 mm, formed under a pressure of about 2 MPa, or toroidals with a outside diameter of 20 mm, an inside diameter of 10 mm and a thickness of 3 mm, formed under a pressure of about 7 MPa). The disks or toroidals are sintered at 890° C. for 4 hours (sample 3-1), 6 hours (sample 3-2), 8 hours (sample 3-3), or 10 hours (sample 3-4).

[0043] Referring to FIG. 5 and FIG. 6, the permeability and quality factor over a range of frequencies are shown for samples 3-1,3-2, 3-3 and 3-4. It is noted that both the initial permeability and quality factor increases with the duration of sintering incubation. The main electric-magnetic properties of those samples are summarized in Table 3, where μ_(i) is initial permeability, Q is quality factor, (μ_(μ))_(rel) is relative temperature coefficient of inductance, and ρ is insulation resistivity. TABLE III Sample Condition μ_(I) Q (300 MHz) (α_(μ))_(rel)(/° C.) ρ (Ω · cm) 3-1 890° C./4 h  4.3 65 8.7 × 10⁻⁷ 1.7 × 10⁸ 3-2 890° C./6 h  4.8 50 1.2 × 10⁻⁶ 2.3 × 10⁸ 3-3 890° C./8 h  4.9 50 1.4 × 10⁻⁶ 3.8 × 10⁸ 3-4 890° C./10 h 5.1 45 2.9 × 10⁻⁶ 5.6 × 10⁸

EXAMPLE 4

[0044] The minor component used here is a mixture of B₂O₃ and PbO. 80.41 grams of FeC₆H₅O₇ 5H₂O dissolved in water. To the solution, 5.82 grams of Co(NO₃)₂.6H₂O and 7.68 grams of Ba(CH₃COO)₂ are added. After adjusting the pH to 6-8 with citric acid and NH₄OH, the solution becomes a dark-brown sol, which is dried up and calcined at an appropriated temperature to produce dark Co₂Z (Z-type hexaferrite) powder. 20 grams of the Co₂Z powder and an appropriate amount of the above defined minor component (a complex of B₂O₃ and PbO) are mixed so that the minor component's weight accounts for 8% (sample 4-1), 10% (sample 4-2), or 12% (sample 4-3). The mixture is ground with iron balls, dried, and pressed into either disks or toroidals (disks with a outside diameter of 10 mm and a thickness of 1 mm, formed under a pressure of about 2 MPa, or toroidals with a outside diameter of 20 mm, an inside diameter of 10 mm and a thickness of 3 mm, formed under a pressure of about 7 MPa). The disks or toroidals are sintered at 890° C. for 6 hours.

[0045] Referring to FIG. 7 and FIG. 8, the permeability and quality factor over a range of frequencies are shown for samples 4-1,4-2, and 4-3. It is noted that the initial permeability decreases as the percentage of minor component increases. The main electric-magnetic properties of those samples are summarized in Table 4, where μ_(i) is initial permeability, Q is quality factor, (α_(μ))_(rel) is relative temperature coefficient of inductance, and ρ is insulation resistivity. TABLE IV Sample Condition μ_(I) Q (300 MHz) (α_(μ))_(rel)(/° C.) ρ (Ω · cm) 4-1 870° C./6 h 3.7 40 2.7 × 10⁻⁶ 3.5 × 10⁹ 4-1 870° C./6 h 3.4 50 1.1 × 10⁻⁶ 2.8 × 10⁹ 4-3 870° C./6 h 2.6 50 1.3 × 10⁻⁶ 9.6 × 10⁸

EXAMPLE 5

[0046] 96.96 grams of Fe(NO₃)₃.9H₂O are dissolved in water and an appropriate amount of NH₄OH is added to the solution to precipitate Fe(OH)₃. The Fe(OH)₃ precipitate is then dissolved in a solution containing 55 grams of citric acid. Upon the citric acid solution becoming transparent, 3.49 grams of Co(NO₃)₂.6H₂O, 1.45 grams of Cu(NO₃)₂.3H₂O, 0.6 grams of Zn(NO₃)₂.H₂O and 7.68 grams of Ba(CH₃COO)₂ are added. After adjusting the pH to 6-8, the solution becomes a dark-brown sol, which is dried and calcined to produce black Z—Cu6Zn2 powder in formula Ba₃CO_(2-x-y)Zn_(x)Cu_(y)Fe₂₄O₄₁, wherein x=0.2, y=0.6 20 grams of the Z—Cu6Zn2 powder is dispersed into ethylene glycol and an appropriate amount of Bi(NO₃)₃ (minor component) added, forming a slurry therein. The minor component should account for 2-4% by weight. The slurry is adjusted to a pH value of 7, dried, and pressed into either a disk form or a toroidal form (disks with a outside diameter of 10 mm and a thickness of 1 mm, formed under a pressure of about 2 MPa, or toroidals with a outside diameter of 20 mm, an inside diameter of 10 mm and a thickness of 3 mm, formed under a pressure of about 7 MPa). The disks or toroidals are sintered at 890° C. (sample 5-1) or 920° C. (sample 5-2) for 6 hours.

[0047] The permeability and quality factor over a range of frequencies for samples 5-1 and 5-2 are shown in FIG. 9. The main electric-magnetic properties of those samples are also summarized in Table 5, where μ_(i) is initial permeability, Q is quality factor, (α_(μ))_(rel) is relative temperature coefficient of inductance, and ρ is insulation resistivity. TABLE V Sample Condition μ_(I) Q (300 MHz) (α_(μ))_(rel)(/° C.) ρ (Ω · cm) 5-1 890° C./6 h 5.3 40 6.7 × 10⁻⁷ 1.6 × 10⁸ 5-1 920° C./6 h 6.0 45 8.9 × 10⁻⁷ 1.7 × 10⁸

EXAMPLE 6

[0048] 96.96 grams of Fe(NO₃)₃.9H₂O are dissolved in water and an appropriate amount of NH₄OH is added to the solution to precipitate Fe(OH)₃. The Fe(OH)₃ precipitate is then dissolved in a solution containing 55 grams of citric acid. Upon the citric acid solution becoming transparent, 4.07 grams of Co(NO₃)₂.6H₂O, 1.45 grams of Cu(NO₃)₂.3H₂O, and 7.68 grams of Ba(CH₃COO)₂ are added. After adjusting the pH to 6-8, the solution becomes a dark-brown sol, which is dried and calcined to produce black Z—Cu6 powder in formula Ba₃CO_(2-x-y)Zn_(z)Cu_(y)Fe₂₄O₄₁. 20 grams of the Z—Cu6 powder is dispersed into ethylene glycol and an appropriate amount of Bi(NO₃)₃ (minor component) added, forming a slurry therein. The minor component should account for 4% by weight. The slurry is adjusted to a pH value of 7, dried, and pressed into either a disk form or a toroidal form (disks with a outside diameter of 10 mm and a thickness of 1 mm, formed under a pressure of about 2 MPa, or toroidals with a outside diameter of 20 mm, an inside diameter of 10 mm and a thickness of 3 mm, formed under a pressure of about 7 MPa). The disks or toroidals are sintered at 890° C. (sample 6-1) or 920° C. (sample 6-2) for 6 hours.

[0049] The permeability and quality factor over a range of frequencies for samples 6-1 and 6-2 are shown in FIG. 10. The main electric-magnetic properties of those samples are also summarized in Table 6, where μ_(i) is initial permeability, Q is quality factor, (α_(μ))_(rel) is relative temperature coefficient of inductance, and ρ is insulation resistivity.

[0050] In this example, the amounts of the precursor compounds can be varied to produce a modified Co₂Z hexaferrite in formula Ba₃Co_(2-x-y)Zn_(x) Cuy Fe₂₄O₄₁, wherein X=0.4 and y=0.4 (x and y are defined elsewhere in this disclosure). Using this Co₂Z hexaferrite and follow the same produce described in the preceding paragraphs of this example, disks or toroidals of the same dimentions can be produced and sintered at 890° C. (sample 9-2) for 6 hours.

[0051] The premeability and quality factor over a range of frequencies for samples 9-1 and 9-2 are shown in FIG. 13. The main electric-magnetic properties of those samples are also summarized in Table 9, where μ_(I) is initial permebility, Q is quality factor, ( )_(rei) is relative temperature coefficient of inductance, and is insulation resistivity. TABLE VI Sample Condition μ_(I) Q (300 MHz) (α_(μ))_(rel)(/° C.) ρ (Ω · cm) 6-1 890° C./6 h 4.8 40 1.0 × 10⁻⁶ 7.8 × 10⁸ 6-2 920° C./6 h 5.9 40 2.3 × 10⁻⁶ 5.9 × 10⁸

[0052] TABLE IX Sample Condition μ_(I) Q (300 MHz) (α_(μ))_(rel)(/° C.) ρ (Ω · cm) 9-1 890° C./6 h 7.7 40 3.3 × 10⁻⁶ 6.6 × 10¹⁰ 9-2 920° C./6 h 8.3 40 3.4 × 10⁻⁶ 9.3 × 10¹⁰

EXAMPLE 7

[0053] 80.41 grams of FeC₆H₅O₇.5H₂O are dissolved in water. To the solution, 5.82 grams of Co(NO₃)₂.6H₂O and 7.68 grams of Ba(CH₃COO)₂ are added. After adjusting the pH to 6-8, the solution becomes a dark-brown sol, which is dried and calcined to produce black Z-type hexaferrite powder. 20 grams of the hexaferrite powder is dispersed into ethylene glycol and an appropriate amount of Bi(NO₃)₃ (minor component) added, forming a slurry therein. The minor component should account for 4% by weight. The slurry is adjusted to a pH value of 7, dried, and pressed into either a disk form or a toroidal form (disks with a outside diameter of 10 mm and a thickness of 1 mm, formed under a pressure of about 2 MPa, or toroidals with a outside diameter of 20 mm, an inside diameter of 10 mm and a thickness of 3 mm, formed under a pressure of about 7 MPa). The disks or toroidals are sintered at 890° C. (sample 7-1) or 920° C. (sample 7-2) for 6 hours.

[0054] The permeability and quality factor over a range of frequencies for samples 7-1 and 7-2 are shown in FIG. 11. The main electric-magnetic properties of those samples are also summarized in Table 7, where μ_(i) is initial permeability, Q is quality factor, (α_(μ))_(rel) is relative temperature coefficient of inductance, and ρ is insulation resistivity. TABLE VII Sample Condition μ_(I) Q (300 MHz) (α_(μ))_(rel)(/° C.) ρ (Ω · cm) 7-1 890° C./6 h 4.4 50 5.4 × 10⁻⁷ 6.1 × 10⁸ 7-2 920° C./6 h 5.2 50 7.1 × 10⁻⁷ 9.5 × 10⁸

EXAMPLE 8

[0055] A complex minor component is used in this embodiment, which comprises Bi(NO₃)₃, Li₂(CH₃COO) and Ca(NO₃)₂ (ratio 1:1:1 by weight). 80.41 grams of FeC₆H₅O₇ 5H₂₀ are dissolved in water. To the solution, 3.49 grams of Co(NO₃)₂.6H₂O, 1.45 grams of Cu(NO₃)₂.3H₂O, 0.6 grams of Zn(NO₃)₂.H₂O and 7.68 grams of Ba(CH₃COO)₂ are added. After adjusting the pH to 6-8, the solution becomes a dark-brown jelly, which is dried and calcined to produce black Z—Cu6Zn2 powder in formula Ba₃CO_(2-x-y) Zn_(x)Cu_(y)Fe₂₄O₄₁ wherein x=0.2 and y=0.6. 20 grams of the hexaferrite powder is dispersed into ethylene glycol and an appropriate amount of the above-specified minor component is added, forming a slurry therein. The minor component should account for 3% by weight. The slurry is adjusted to a pH value of 7, dried, and pressed into either a disk form or a toroidal form (disks with a outside diameter of 10 mm and a thickness of 1 mm, formed under a pressure of about 2 MPa, or toroidals with a outside diameter of 20 mm, an inside diameter of 10 mm and a thickness of 3 mm, formed under a pressure of about 7 MPa). The disks or toroidals are sintered at 890° C. (sample 8-1) or 920° C. (sample 8-2) for 6 hours.

[0056] The permeability and quality factor over a range of frequencies for samples 7-1 and 7-2 are shown in FIG. 12. The main electric-magnetic properties of those samples are also summarized in Table 8, where μ_(i) is initial permeability, Q is quality factor, (α_(μ))_(rel) is relative temperature coefficient of inductance, and ρ is insulation resistivity. TABLE VIII Sample Condition μ_(i) Q (300 MHz) (α_(μ))_(rel)(/° C.) ρ (Ω · cm) 8-1 890° C./6 h 4.3 50 2.7 × 10⁻⁶ 3.5 × 10⁸ 8-2 920° C./6 h 4.8 45 1.5 × 10⁻⁶ 5.2 × 10⁸

EXAMPLE 9

[0057] In this embodiment, Z—Mn2 hexaferrite in formula Ba₃CO_(2-x-y) Zn_(x)Cu_(y)Fe₂₄O₄₁, (wherein Z=0.2, W=0.8) is the major component. The minor component comprises Bi₂O₃ and V₂O₅ (ratio of 1:1 by weight). 92.2 grams of Fe(NO₃)₃ 9H₂O are dissolved in water and an appropriate amount of NH₄OH is added to precipitate Fe(OH)₃. The Fe(OH)₃ precipitate is then dissolved in a solution containing 55 grams of citric acid. Upon the citric acid solution becoming transparent, 5.82 grams of Co(NO₃)₂ 6H₂O, 7.68 grams of Ba(CH3COO)2 and 0.358 gram of Mn(NO₃)2 are added. After adjusting the pH to 6-8, the solution becomes a dark-brown sol, which is dried and calcined at an appropriated temperature to produce dark Z—Mn2 hexaferrite powder, 20 grams of the powder and an appropriate amount of the above defined minor component are mixed so that the weight percentage of the minor component is 2.0%. The mixture is ground, dried and pressed into either disks or torodials (disk with an outside diameter of 10 mm and a thickness of 1 mm, formed under a pressure of about 2 Mpa, or torodials with an outside diameter of 20 mm, an inside diameter of 10 mm and a thickness of 3 mm, formed under a pressure of about 7 Mpa). The disks or torodials are sintered at 870° C. (sample 10-1), 890° C. (sample 10-2) and 920° C. (sample 10-3).

[0058] The foregoing examples demonstrate that the new material prepared according to the present invention using lower sintering temperatures represents significant improvement in sintering behavior, homogeneity of grain size, density, initial permeability, quality factor, insulation resistivity and natural ferromagnetic resonance at frequencies over 1.0 GHz. Therefore, it process a great potential as a soft magnetic material for manufacturing hfMLCIs.

[0059]FIG. 14 shows the permeability and quality factor over a range of frequencies for samples 10-1, 10-2 and 10-3. For all the samples the initial permeability is above 4 and the quality factor at 300 MHz is above 60. The main electric-magnetic properties of the samples are also summarized in table 10, where μ_(I) is the initial permeability, Q is quality factor, (α_(μ))_(rel) is relative temperature coefficient of inductance, and ρ is insulation resistivity TABLE X Sample Condition μ_(I) Q (300 MHz) (α_(μ))_(rel)(/° C.) ρ (Ω · cm) 10-1 890° C./6 h 4.2 80 2.5 × 10⁻⁶ 7.8 × 10⁸ 10-2 920° C./6 h 4.3 90 1.8 × 10⁻⁶ 9.5 × 10⁸ 10-3 950° C./6 h 4.7 60 1.7 × 10⁻⁶ 1.2 × 10⁹

[0060] The foregoing examples demonstrate that the new material prepared according to the present invention using lower sintering temperatures represents significant improvement in sintering behavior, homogeneity of grain size, density, initial permeability, quality factor, insulation resistivity and natural ferromagnetic resonance at frequencies over 1.0 GHz. Therefore, it process a great potential as a soft magnetic material for manufacturing hfMLCIs.

[0061] Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto. 

We claim:
 1. A composition of hyper frequency (hf) multilayer chip inductors (MLCI) materials comprising:: the major component Z-type planar hexaferrite as following: BA₃Co_(2-x-y-)Zn_(x)Cu_(y)Mn_(z)Fe_(24-z-w-)O_(41-3/2(Z+W)), wherein: 0≦x≦1.0; 0≦y≦0.80; ≦z≦1.0; and 0≦w≦; 1.0; and the minor component used as sintering aid as following: aBi₂O₃ +bV₂O₅ +cPbO+dB₂O₃ +eLiF+FCaF₂. wherein: 0≦a≦1 0<b<1; 0≦c≦1; ≦d≦1; 0≦e≦1; 0≦f≦1; it the weight ratio of the major component to the minor component is between 98:2 to 88:12.
 2. A method of preparing the hf MLCI materials as described in claim 1 comprising the following steps: a) synthesizing Z-type planar hexaferrite using inorganic iron salt as raw materials: step 1: putting Fe3^(˜) iron salt into an aqueous solution before being precipitated by a ammonia solution to form precipitate Fe(OH)3. step 2: after filtering, washing, dissolving the fresh Fe(OH)3 precipitate into hot citric acid solution at 60-800 C. with Fe/citric acid mole ratio in 1 to 2, obtaining a transparent solution; step 3: putting cobalt, barium, zinc, copper and manganese acetate or nitrate salts in stoichiometric quantities to said solution in step 2, and then dropping an appropriate ammonia until the said solution being neutral or slightly alkaline (pH '6-8) for 2 hours to give a stable sol containing the required Co2Z type hexaferrite composition; step 4: drying said sol at 130-150 “C. for 6-10 h, and then heating-treated at a temperature between 900 to 1250 ”C. for 6 h, resulting in Z-type hexaferrite powders; b) the sintering aids being mixed with hexaferrite powders by conventional ceramic route: step 5: mixing the said hexaferrite powders with sintering aids oxides Bi2O3 . . . V205 in a ball mill for 4 hours according the composition mentioned above during a medium of water or alcohol to form a slurry; step 6: drying said slurry at 80-120 “C., then sieving the powders, pressing them into pellets; step 7: sintering said pellets at 870-950 C. for 2-6 h, obtaining the said hyper frequency MLCI materials.
 3. A method of preparing the hfMLCI materials as described in claim 1 comprising the following steps: a) synthesizing Z-type planar hexaferrite using organic iron salt such as iron citrate as raw materials: step 1: dissolving iron citrate into aqueous solution, before mixing with barium, cobalt, zinc, copper and manganese acetate or nitrate salts in stoichiometric quantities to get a mixed solution; step 2: dropping appropriate amount of ammonia solution into the said mixed solution to make it neutral or slightly alkaline (pH=6-8), obtaining a steady sol; step 3: drying the said sol at 130 to 150 “C. for 6 to 10 h, then heating treated between 900-1250 ”C. for 6 h, resulting in Z-type hexaferrite powders; b) the sintering aids being mixed with hexaferrite powders by conventional ceramic route: step 4: mixing the said hexaferrite powders with sintering aids oxides Bi2O3 V205 in a ball mill for 4 hours according the composition mentioned above during a 16 medium of water or alcohol to form a slurry; step 5: drying said slurry at 80-120° C., then sieving the powders, pressing them into pellets; step 6: sintering said pellets at 870-^(˜)950° C. for 2-6 h, obtaining the said hyper frequency MLCI materials.
 4. A method of preparing the hf MLCI materials as described in claim 1 comprising the following steps: a) synthesizing Z-type planar hexaferrite using inorganic iron salt as raw materials: step 1: putting Fe³⁺ iron salt into an aqueous solution before being precipitated by a ammonia solution to form precipitate Fe(OH)3. step 2: after filtering, washing, dissolving the fresh Fe(OH)3 precipitate into hot citric acid solution at 60-80° C. with Fe/citric acid mole ratio in 1 to 2, obtaining a transparent solution; step 3: putting cobalt, barium, zinc, copper and manganese acetate or nitrate salts in stoichiometric quantities to said solution in step 2, and then dropping an appropriate ammonia until the said solution being neutral or slightly alkaline (pH 6-8) for 2 hours to give a stable sol containing the required Co2Z type hexaferrite composition; step 4: drying said sol at 130-150 “C. for 6^(˜)10 h, and then heating-treated at a temperature between 900 to 1250 ”C. for 6 h, resulting in Z-type hexaferrite powders; b) the sintering aids being added into hexaferrite powders by chemical coating route as the following: step 5: dispersing the said hexaferrite powders into ethylene glycol to form a slurry, blending the sintering aids in water-soluble forms into the slurry, adjusting pH value of the mixed slurry so as to the sintering aids coating on the surface of hexaferrite particles in forms of hydroxides; step 6: after drying the mixed slurry, calcining it at 700° C. for 2 h to form a second hexaferrite powders containing sintering aids; step 7: sieving, pressing the second powders and sintering them at 870^(˜)950 C. for 6 h, obtaining the invented hyper frequency MLCI materials.
 5. A method of preparing the hf MLCI materials as described in claim 1 comprising the following steps: a) synthesizing Z-type planar hexaferrite using organic iron salt such as iron citrate as raw materials: step 1: dissolving iron citrate into aqueous solution, before mixing with barium, cobalt, zinc, copper and manganese acetate or nitrate salts in stoichiometric quantities to get a mixed solution; step 2: dropping appropriate amount of ammonia solution into the said mixed solution for 6 to 8 hours to make it neutral or slightly alkaline (pH=6-8), obtaining a steady sol; step 3: drying the said sol at 130 to 150 “C. for 6 to 10 h, then heating treated between 900^(˜)1250 ”C. for 6 h, resulting in Z-type hexaferrite powders; b) the sintering aids being added into hexaferrite powders by chemical coating route as the following: step 4: dispersing the said hexaferrite powders into ethylene glycol to form a slurry, blending the sintering aids in water-soluble forms into the slurry, adjusting pH value of the mixed slurry so as to the sintering aids coating on the surface of hexaferrite particles in forms of hydroxides; step 5: after drying the mixed slurry, calcining it at 700 “C. for 2 h to form a second hexaferrite powders containing sintering aids; step 6: sieving, pressing the second powders and sintering them at 870^(˜)950 ”C. for 6 h, obtaining the invented hyper frequency MLCI materials. 